Thank you Lifehacker.com for this one. You wont need to download anything here. Just type the following into Terminal, and the game will launch automatically.
emacs -batch -l dunnet
If youve never played a MUD before, you’ll find that its actually pretty intuitive. For example, you start the game standing on a road with a shovel nearby. Type “take shovel” to add the shovel to your inventory, and “go east” to walk down the road. Typing “Inventory” will show you what youre carrying, “save” and “restore” let you play through in multiple sessions, and “help” gives you some tips if youre stuck. Id also recommend using some scratch paper to map out the area as you discover it. Check out the source link for a few other Terminal easter eggs to help you kill some time this weekend.
via Discover the Text-Based Adventure Game Built Into Your Macs Terminal.